The dimensions of asthma as a public health problem in the United States cannot be precisely defined due in part to the relative paucity of longitudinal incidence, survival, and mortality data. This project is a descriptive, population-based, epidemiologic study of asthma in the city of Rochester, Minnesota. Using an existing computerized diagnostic index, we will: a) identify all Rochester residents who have sought medical care for asthma between 1964 and 1984; b) estimate the incidence of new asthma cases by age and sex for each five-year interval from 1964 to 1984; c) determine whether the age- and sex-adjusted incidence, survival, or mortality of asthma has changed over the study period; d) test the hypothesis that the natural history of asthma differs by sex and age of onset, particularly for asthma beginning after the age of 40; e) identify fatal cases of asthma, an define the relationship of reported to actual deaths for asthma, and calculate mortality rates for reported deaths and actual asthma deaths. Asthma cases will be identified by searching the computerized index for persons with recorded diagnoses of bronchial asthma, asthmatic bronchitis, chronic allergic bronchitis, allergic (extrinsic) asthma, or nonallergic (intrinsic) asthma. The unit medical records of all such patients will be thoroughly reviewed by trained nurse abstractors who, using predefined criteria, will classify the patient as having or not having asthma. A random sample of patient records with other diagnoses (chronic obstructive pulmonary disease, recurrent bronchitis, chronic cough, etc.) will also be reviewed to identify additional diagnostic categories that require screening. The availability of the computerized diagnostic index and medical record linkage system should permit identification of greater than 95% of asthmatics in the community. Thus, the population-based approach proposed will provide much more precise estimates of the incidence of asthma and more reliable information on the natural history of asthma (especially in persons over age 400 than have cross-sectional community studies reported previously.